I applaud your commitment to fighting climate change. Your administration's new carbon pollution limits for power plants are a giant step in the right direction and demonstrate that America is ready to move forward on climate. In a year of record-breaking wildfires, floods, and other symptoms of a disrupted climate, your leadership on climate change is exactly what our country needs.

I am concerned that this progress may be undermined by a backdoor bilateral agreement on the proposed Keystone XL tar sands pipeline that would commit us to transporting the dirtiest of fossil fuels for decades to come. Several weeks ago, Canadian Prime Minister Stephen Harper reportedly sent you a letter declaring his willingness to take any climate actions necessary to get a presidential approval of Keystone XL, the $7-billion pipeline that would pump Alberta tar sands to Gulf Coast refineries. While this may seem like a generous offer, Canada simply cannot mitigate the carbon pollution from the pipeline; those emissions would simply be too big. Keystone XL would be directly responsible for the equivalent annual emissions of 51 coal-fired power plants or 37.7 million cars. As a point of comparison, Canada has about 26 million cars on the road.

Along with the pipeline's direct emissions, the pipeline would be responsible for decades of future emissions from tar sands. The Pembina Institute estimates that Keystone XL would increase tar sands development by 36 percent. The State Department estimates that tar sands oil could be 22 percent more carbon intensive than conventional crude used in the United States. And when the lost carbon sequestration potential of Canada's 1.2 billion acre boreal forest is also taken into consideration, the climate implications of the pipeline become staggering. The best way to "mitigate" tar sands development is to keep tar sands in the ground.

Promises by Prime Minister Stephen Harper's government to reduce the emissions from Canada’s tar sands should be judged against its failure to live up to its climate commitments to date. The government of Canada has consistently missed its own targets to regulate its oil and gas sector and reduce national emissions, and has a history of weakening environmental regulations at the request of the pipeline industry. The Canadian government eliminated the budget for its National Roundtable on Energy and the Environment after it advocated a carbon tax. In addition, the government of Canada is silencing its scientists, as highlighted in last weekend's New York Times when the paper noted, "There was trouble of this kind here in the George W. Bush years....But nothing came close to what is being done in Canada." Even if mitigating carbon pollution from the tar sands pipeline were possible, the Harper administration has shown no signs that it would be willing to do it.

The fact is, tar sands are Canada's fastest-growing source of carbon pollution. In 2011, the Canadian government's own peer-reviewed reports forecasted that emissions from tar sands would be triple 2005 levels by 2030. The Canadian government’s promises to offset tar sands carbon pollution are nothing more than a rubber check written against an empty account. That check would bounce, just like all of the Harper government's other climate promises. The one thing climate scientists and energy experts say we can be sure of, is that the Keystone XL pipeline would deliver a massive new source of carbon pollution.

Mr. President, a national interest determination decision on the Keystone XL pipeline must not be premised on the government of Canada's mitigation promises. We urge you to reject the pipeline and continue to help build a clean energy future.

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